1. Field of the Invention
The present invention relates to a megasonic cleaning module, and, more particularly, to a megasonic cleaning module including a vibrator having a piezoelectric element, to which power is supplied from a power supply unit, mounted therein for generating ultrasonic waves by the vibration of the piezoelectric element, a first vibratory rod coupled to one side of the vibrator such that the first vibratory rod is vertically located above one major surface of a semiconductor wafer to be cleaned, the first vibratory rod having a diameter gradually decreased to concentrate the longitudinal ultrasonic waves generated from the vibrator, and a second vibratory rod coupled to the first vibratory rod, such that the second vibratory rod is perpendicular to the first vibratory rod, for progressing the longitudinal ultrasonic waves, generated from the first vibratory rod, in the transverse direction, wherein the size of the second vibratory rod at one side thereof where the second vibratory rod is coupled to the first vibratory rod is less than that of the second vibratory rod at the other side thereof, with the result that the longitudinal ultrasonic waves are not prevented from affecting the wafer, and the second vibratory rod has various sectional shapes at the other side thereof, thereby effectively separating foreign matter from the wafer using the transverse ultrasonic waves.
2. Description of the Related Art
One of the most fundamental technologies in a semiconductor manufacturing process is a cleaning technology. The semiconductor manufacturing process includes several steps to form the surface of a semiconductor wafer. At the respective steps, various contaminants are generated and attached to both a semiconductor wafer and a semiconductor manufacturing apparatus. For this reason, it is necessary to clean the semiconductor wafer and the semiconductor manufacturing apparatus at predetermined time intervals. Therefore, the cleaning technology is designed to remove several contaminants, generated during the semiconductor manufacturing process, using a physical or chemical method.
The chemical method is to remove the contaminants from the surface of a semiconductor wafer using washing, etching, and an oxidation-reduction reaction. In this case, various chemicals or gases are used. In the chemical method, particles, attached to the surface of the semiconductor wafer, are removed by a pure or chemical cleaning liquid. Organic matter is dissolved by a solvent, is removed by an oxidizing acid, or is carbonized by oxygen plasma. According to circumstances, the surface of the semiconductor wafer is partially etched such that a new clean surface portion is exposed to the outside.
The physical method is to separate matter from the surface of the semiconductor wafer using ultrasonic energy, to wipe matter out from the surface of the semiconductor wafer using a brush, or to remove matter from the surface of the semiconductor wafer using high-pressure water. Generally, the physical method is used jointly with the chemical method to accomplish more efficient cleaning.
The ultrasonic cleaning is to remove contaminants from an object to be cleaned by a physical means (ultrasonic waves) and a chemical means (a chemical cleaning liquid) and to prevent the removed contaminants from being attached again to the surface of the object. The physical phenomenon by the ultrasonic waves occurs through a cavitation phenomenon of the ultrasonic waves. The cavitation phenomenon is a phenomenon in which, when ultrasonic energy is transmitted into the liquid, micro air bubbles are generated and extinguished by the pressure of the ultrasonic waves. The cavitation phenomenon is accompanied by high pressure (several tens to hundreds of atmospheric pressure) and high temperature (several hundreds to thousands of degrees).
This phenomenon repeatedly occurs and disappears for an extremely short period of time (one over tens of thousands to one over hundreds of thousands of seconds). By these shock waves, the cleaning is performed even to the invisible inside region of the object soaked in the liquid within a short period of time.
Practically, the stirring effect and thermal effect due to the radiation pressure of the ultrasonic waves cause synergism together with detergent in addition to the impact energy due to the cavitation, with the result that the cleaning efficiency is further improved.
The ultrasonic cleaning is used generally to clean or rinse an object to be cleaned, such as a glass substrate for liquid crystal displays (LCD), a semiconductor wafer, or a magnetic disk for data storage. In a general ultrasonic cleaning system, an object to be cleaned is introduced into a cleaning tub containing cleaning liquid, to which ultrasonic waves are applied from a vibratory plate actuated by an ultrasonic vibrator. The ultrasonic waves apply vibratory energy to particles on the object such that the particles and other contaminants are effectively removed from the object.
With the recent high integration of a semiconductor device, a pattern, which will be formed on a wafer, becomes very small. As a result, the pattern on the wafer causes the defect of the semiconductor device due to even micro particles. Consequently, the importance of the cleaning process is being more and more highlighted.
Generally, the wafer cleaning is carried out using ultra pure water (cleaning liquid), a brush, and ultrasonic waves.
FIG. 1 is a view illustrating the structure of a conventional ultrasonic apparatus for cleaning a semiconductor. The conventional ultrasonic cleaning apparatus cleans the surface of a semiconductor wafer 105 using ultrasonic waves and cleaning water (or cleaning liquid). The ultrasonic cleaning apparatus includes a cleaning water sprayer 106, the lower end of which is formed in the shape of a nozzle. Cleaning water 103 is supplied into the cleaning water sprayer 106 through a supply pipe 102 connected to one side of the cleaning water sprayer 106.
When the cleaning water 103 is introduced into the cleaning water sprayer 106 through the supply pipe 102, ultrasonic waves are generated from a vibration unit 101. As a result, the cleaning water 103, carrying the ultrasonic waves, is sprayed to an object to be cleaned, which is located below the cleaning water sprayer 106. At this time, the object is rotated by a rotary shaft 104. Consequently, the surface of the object is cleaned.
In the conventional ultrasonic cleaning apparatus, however, the cleaning water 103, carrying the ultrasonic waves, is sprayed from the single cleaning water sprayer 106. As a result, the cleaning efficiency is low although the cleaning water 103 is excessively consumed.
Also, the intensity of the ultrasonic waves is greatly changed due to instantaneous fluctuation of the cleaning conditions, such as the operational frequency, the condition of the cleaning water, the power consumption, and the cooling condition, during the cleaning process. Furthermore, the high-pressure cleaning water is sprayed through the nozzle structure, with the result that the surface of the semiconductor wafer is locally or entirely damaged.
FIG. 2 is a view illustrating the structure of another conventional ultrasonic cleaning apparatus for cleaning a semiconductor using a vibratory rod. The conventional ultrasonic cleaning apparatus includes a vibratory rod 110 protruding forward and arranged such that the vibratory rod 110 is spaced a predetermined gap from a semiconductor wafer 114, which is located below the vibratory rod 110, a vibration unit 111 coupled to the vibratory rod 110 for supplying ultrasonic oscillation energy to the vibratory rod 110, and a cleaning water sprayer 113 for spraying cleaning water 116 into the gap between the vibratory rod 110 and the semiconductor wafer 114.
The conventional ultrasonic cleaning apparatus further includes a rotary plate 112 and a rotary shaft 115 for rotating the semiconductor wafer 114. The semiconductor wafer 114 is placed on the rotary plate 112, and the vibratory rod 110 is located above the semiconductor wafer 114. Consequently, the vibratory rod 110 generates ultrasonic waves in the form of longitudinal waves while the semiconductor wafer 114 is rotated by the rotary plate 112 and the rotary shaft 115, with the result that, when the cleaning water 116 is sprayed to the semiconductor wafer 114, the ultrasonic cleaning is performed to the entire surface of the semiconductor wafer 114.
In the conventional ultrasonic cleaning apparatus for cleaning the semiconductor using the vibratory rod as shown in FIG. 2, however, the vibratory rod 110 is mounted in a cantilever type structure, with the result that the cleaning process is performed only below the axial direction of the vibratory rod 110. Consequently, strength and weakness of the ultrasonic waves occur structurally along the vibratory rod 110, whereby uniform cleaning efficiency is not expected on a wafer having a micro pattern.